Bovine mastitis is the most frequent and costly disease for dairy producers and Staphylococcus aureus is considered to be the transmittable bacterium that is the most often responsible for the development of the disease (Sears et al., 2003). Staphylococcal intramammary infections (IMI), which may lead to mastitis, are difficult to treat and frequent relapses are common (Sandholm et al., 1990). Bacterial susceptibility to antibiotics in vitro is a poor predictor of therapeutic efficacy in chronically infected cows (Owens et al., 1997). Although infections that follow treatment of mastitis can be due to newly acquired strains, they are often the result of the persistence of the original infective organism (Sandholm et al., 1990; Myllys et al., 1997). Existing therapies thus often fail to eliminate the infection and it would be highly desirable to find novel approaches to prevent or treat staphylococcal IMI.
A lack of vaccine efficacy and protective ability has been noted for commercially available S. aureus vaccines (Middleton, 2008). A number of additional Staphylococci vaccines and vaccine components have been described and proposed. The use of milk or low-iron media as surrogate systems for exploring S. aureus genes that are expressed during IMI do not fully replicate the actual mammalian host environment that may vary in nutrient composition, in interactions with host cells and in immune response components, to name just a few differences. Hence, the S. aureus components currently proposed as vaccine are not necessarily the components that are expressed during IMI at multiple points in time, by multiple strains (including chronic strains) and in multiple hosts. Thus it would be highly desirable to identify S. aureus genes that are expressed during IMI at multiple points in time, by multiple strains, and in multiple hosts, so that a selection of genes and gene-encoded products (e.g., proteins) can be used either alone or in combination for protection against IMI and mastitis.
The present invention seeks to meet these and other needs.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.